Communication network operators give highest priority to Emergency Calls (EC). With wide spread use of mobile phones communication networks need to have an enhanced emergency call handling infrastructure across cells. The emergency call handling infrastructure should be able to provide emergency call continuity for a roaming user. The inbound mobility refers to a network controlled, handover functionality for User Equipment (UE) in Radio Resource Control (RRC) connected state with an established connection to the network.
In Long Term Evolution (LTE) as per third generation partnership project (3GPP) standard the networks support handover of the calls across the cells. The UE in connected mode measures only the cells on frequencies configured by the network and reports the measurement results based on event or on periodical reporting criteria. Autonomous search procedure allows the UE to search for the Closed Subscriber Group (CSG) cells present on those frequencies, for which the UE is not configured by the network. As per 3GPP specifications, 36.331 and 36.304, the UE in connected mode starts the autonomous search procedure only when the network configures the UE for proximity reporting. The UE can transmit proximity report for the detected CSG cell only if the CSG cell is present in its CSG whitelist (member CSG cell).
Moreover, in the existing methods the UE reports proximity indication of the detected member CSG cell even though the member CSG cell fails to support emergency call service. The UE follows the autonomous search procedure irrespective of type of the call, which can be an emergency call or a normal (regular) call. With existing method, the UE is unable to utilize available services of the non-member CSG cell which is not part of its white list. Thus, the UE never reports proximity of the detected non-member CSG cell to the network. If the UE fails to detect another member CSG cell the emergency call maybe discontinued.
Due to above mentioned reasons, existing methods following the 3GPP standard specification 36, fail to provide emergency call continuity in non-member CSG cells. The existing method relies on the network to configure the UE for initiating autonomous search procedure and delay in the process may result in discontinuation of the emergency call.